1. Field of the Technology
This invention relates generally to three terminal magnetic sensors (TTMs) suitable for use in magnetic heads, which includes spin valve transistors (SVTs), magnetic tunnel transistors (MTTs), or double junction structures.
2. Description of the Related Art
Magnetoresistive (MR) sensors have typically been used as read sensors in hard disk drives. An MR sensor detects magnetic field signals through the resistance changes of a read element, fabricated of a magnetic material, as a function of the strength and direction of magnetic flux being sensed by the read element. The conventional MR sensor, such as that used as a MR read head for reading data in magnetic recording disk drives, operates on the basis of the anisotropic magnetoresistive (AMR) effect of the bulk magnetic material, which is typically permalloy. A component of the read element resistance varies as the square of the cosine of the angle between the magnetization direction in the read element and the direction of sense current through the read element. Recorded data can be read from a magnetic medium, such as the disk in a disk drive, because the external field from the recorded magnetic medium (the signal field) causes a change in the direction of magnetization in the read element, which causes a change in resistance of the read element and a resulting change in the sensed current or voltage.
A three terminal magnetic sensor (TTM) of a magnetic head may comprise a spin valve transistor (SVT), for example, which is a vertical spin injection device having electrons injected over a barrier layer into a free layer. The electrons undergo spin-dependent scattering, and those that are only weakly scattered retain sufficient energy to traverse a second barrier. The current over the second barrier is referred to as the magneto-current. Conventional SVTs are constructed using a traditional three-terminal framework having an “emitter-base-collector” structure of a bipolar transistor. SVTs further include a spin valve (SV) on a metallic base region, whereby the collector current is controlled by the magnetic state of the base region using spin-dependent scattering. Although the TTM may involve an SVT where both barrier layers are Schottky barriers, the TTM may alternatively incorporate a magnetic tunnel transistor (MTT) where one of the barrier layers is a Schottky barrier and the other barrier layer is a tunnel barrier, or a double junction structure where both barrier layers are tunnel barriers.
The revolution in magnetic storage technology has been led by miniaturization of every component in the system, especially the mechanical fly height. A slider may provide a fly height of less than 10 nanometers, for example. In the prior art, the collector region of a TTM is typically formed as part of a slider body of the hard disk drive. Even though the slider body may be very small, the slider body is much larger than that needed as the collector region for TTM operation.
Based on these relative dimensions, it has been identified that an inherent capacitance between the magnetic media and the collector region/slider body for such small sliders (e.g. Femto sliders) is very large in light of a typical operating frequency of the hard disk drive. For example, the capacitance may be about 18 picofarads (pF) for typical operating frequencies of the hard disk drive of about 1 Gigahertz (Ghz). Such a large capacitance will unnecessarily reduce the signal from the magnetic media and introduce unnecessary noise into the circuit.
Accordingly, there is a need to solve these problems so that TTMs may be suitable for use in these and other devices.